Frost forming on evaporators reduces the efficiency of the heat exchange between the evaporators and the air blown thereon. Refrigerators of all types must be kept at controlled temperatures to preserve the foodstuff in suitable conditions. Moreover, national regulations require that the refrigerators operate at predetermined conditions. Accordingly, it is known to provide various types of defrost systems/configurations for commercially used evaporators. The defrost systems therefore help to keep the evaporators in optimal operative conditions.
One type of defrost system involves the convective defrosting of the evaporators. In convective defrosting, hot air is blown onto the evaporator to melt the frost during a defrost period. The supply of refrigerant is stopped during the defrost period. In order to do so, a valve is provided upstream of the evaporator to cut the refrigerant supply.
Defrost systems of refrigeration systems of supermarkets or large food outlets are often fully automated. The valves that are upstream of the evaporators (e.g., solenoid) are all wired to a central controller that synchronizes the defrost period of the evaporators with the actuation of a heating coil that will warm up the air blown onto the evaporator in defrost mode.
Refrigeration systems with convective defrost systems presently have independent control for each evaporator. This allows the evaporators to each be defrosted individually, for instance while other evaporators are in a normal refrigerating mode. Although they offer the optimal control of the evaporators, these refrigeration systems represent an expensive solution in many ways, including equipment costs (valves at each evaporator, wiring), installation and programming expenses.